Carbon brake body and metal holder unit



Oct. 30, 1945. '0. coNRADTY 2,388,123

CARBON BRAKE BODY AND METAL HOLDER UNIT Fivled May 8*, 1940 [n1/enfer.' Omar Conrad@ Patented Oct. 3 0, 1945 cannon BRAKE BODY AND METAL f Homan UNIT Ottmar Conradty, Bothenbach on the Pegnitz,

Germany; lvested in the Alien Property Custo- Appueaaon May s, 1940, serial No. sanos-1 In Germany March 2,2, 1939 (Cl. 18S-251) 2Claims.

This invention relates to a combined carbon body and metal holder unit of the type used, for example, for contact brushes and more particularly, for brakes.

In units of the type referred to it is diilicult to provide an intimate physical connection between the carbon body and its metal holder. The dimculties arise mainly from the fact that the carbon and metal parts have different physical properties and, more particularly, diilerent coemcients of thermal expansion.

It is an object of the present invention to remove lthese difficulties and to provide a design in which an intimate connection is created and the carbon body is reliably secured to its metal holder without the danger of undue stresses or tensions exerted upon the carbon body by its holder.

With this and further objects in view, as may vbecome apparent from the within disclosures, the

invention consists not only in the structures herein pointed out and illustrated by the drawing, but includes further structures coming within the scope of what hereinafter may be claimed.

The character of the invention, however, may be best understood by reference to certain of its structural forms, as illustrated by .the accompanying drawing in which:

Fig. 1 is a cross sectional view of a known unit oi the type referred to.

Fig. 2 is a longitudinal section through the same unit.

Fig. 3 is a similar View as Fig. 1, out having the invention applied thereto.

Fig. 4 is the same view as Fig. 3, but showing the parts after shrinking of the metal holder.

Figs. 5 and 6 are longitudinal sections of the arrangements of Figs. 3 and 4, respectively.

Similar reference numerals denote similar parts in the different views.

Referring now to the drawing in greater detail, Figs. 1 and 2 show the condition of the carbon body and metal holder as it may result where the holder is cast around the carbon body. Owing to the considerable shrinking pressure exerted upon the carbon material cracks are formed at c and c' which in turn cause the holder to bend round and form spaces as indicated at d. Moreover, due to the longitudinal shrinking the carbon body is bent down whereby the heard of the carbon body is separated from the ioot portion as indicated at c in Fig. 2.

I avoid the said defects by the interposition of an elastic or compressible bolster or insert P between the carbon body b and its holder a, which operation. The bolster may be of a metallic nature and may consist, for example, of soft copper or aluminum texture or sponge of a thickness corresponding to the amount by which the metal holder will shrink as it is cooling down. Accordingly the texture will be made thicker where a strong and large holder is provided and thinner in case of a thin holder. In each case the bolster material must be of a thickness to be completely compressed after the shrinking oi' the metal holder. ByA reason of the shrinking pressure of the surrounding holder-it is tightly and completely pressed against the carbon material b and in addition it is penetrated by the cast metal of the metal holder a.

It will thus be understood that any pressures exerted upon the carbon'body b by the bolster d are compensated by the metal bolster P, whereby a, very intimate connection is attained between the carbon and metal holder material while there are no mechanical tensions any more between the top part oi the carbon body and the dovetail or foot portion thereof.

As shown by` comparison of Figs. 3 and 4, or 5 and 6, respectively, the porous metal bolster P (texture or sponge) of Figs. 3 and 5 is compressed to the dense and much thinner layer P, Figs. 4 and 6 without exerting any excessive pressure upon the carbon body which would cause destruction of the carbon lmaterial in the manner as indicated in Figs. 1 and 2.

Figs. 5 and 6 will also make it clear that there is no bending stress exerted upon the carbon body, owing to the uniform and intimate contact between the holder and the carbon body, ensured by the interposed buffer layer P so that there is no danger for the head portion of the carbon body to burst on.

While the figures are especially designed for a carbon body and metal holder unit of the type used as a trolley brush or collector bow for electric railways and the like, my invention may also be applied with very good success for other pur poses where a carbon body has to be secured in a metal holder or vice versa. For example, brake blocks of carbon material may be secured in metal holders of iron or cast steel material, steel being used with a view to the high stresses produced by the high pressures with which the carbon blocks are forced against the surface to be braked. However, the shrinking coeiiicient of iron and cast steel amounts to about 6%, i. e., it is even much higher than that of light. metals of the Ytype used as a holder material for electric metal 'contact devices. Therefore, the danger of the carbon body being destroyed by the shrinking pressure of the metal holder is even higher in this case., Now, by the provision of intermediate bolster layers of the type above referred to and indicated at P in Figs. 3 6, the

carbon body may be protected against any undue pressures.

It will be understood that the interposed bolster material must be heat-proof up to the temperatures occurring by application of the metal holder to the carbon body. For example, where a cast steel holder is applied, the bolster material must be designed to stand the annealing temperature of cast steel.

Where the carbon bodies are not intended to transmit any electric current, such as in the case of brake blocks, nonmetallic, fire-proof or refractory bolster materials may be used to damp and receive the shrinking pressures of the metal holder. For example, mineral material, asbestos, slag wool, silicate cotton, cinder hair and the like may be used in the form of a texture or loose mass which is compressed as the surrounding metal casting is shrinking together.

It is also contemplated that holsters of the type referred to may be applied where the metal holder is combined with the carbon body in a heated, but solid condition of the holder, by a y mere shrinking operation.

The method and apparatus of the present invention have been described in detail with reference to specific embodiments. It is to be understood, however, that the invention is 'not limited by such specific reference but is broader in scope and'capable of other embodiments than those .specifically described arid illustrated in the drawing.

I claim:

1. A brake shoe having a body of frictional 'carbon material, a box-like metal holder cast around part of said carbon body which is retained in said holder by the shrinkage of the metal in casting, intertting dove-tailed portions being with said body and said holder, respectively, and a compressible bolster interposed between said engaging portions of said holder and said body, whereby said bolster absorbs excessive stresses and shocks during the shrinkage of the metal holder and during the operation of the brake shoe.

2. A brake shoe having a longitudinal member of frictional carbon material, a box-like metal holder cast around said member, said holder being formed with a, body portion, protruding end edge portions and protruding dove-tail side portions, and said member being formed with dovetail recesses into which said dove-tail edge portions t, said member being held in said holder by the shrinkage of the metal and a compressible bolster interposed between said edge portions and member, whereby said bolster absorbs excessive '8o stresses during the shrinkage of said metal holder and shocks and stresses during the operation of 

